Many modern electro-optical and optoelectronic devices include fiber-coupled components. Optical fibers of these components need to be routed within the devices. Optical fibers of different components or modules are coupled together by splicing. The splice locations need to be mechanically protected.
Optical fiber has a number of unique packaging requirements that are different from those of an electrical wire, for example. One such requirement is that of a minimal fiber bending radius. The capability of an optical fiber to guide light is limited. When the optical fiber is bent at a radius less than a so-called minimum bending radius, the fiber begins to leak some light at the bend. Furthermore, the capability of the optical fiber to bend without structural damage is also limited. Most optical fibers are made of thin polymer-coated fused silica strands. When the optical fiber is bent beyond a minimal radius, the fused silica strand can develop microcracks, which can result in a fiber breakage.
Another packaging requirement of optical fibers stems from somewhat random nature of an optical fiber splicing process. It is well known that no two splices are identical, and occasionally, a splicing operation will fail. When this occurs, an operator usually breaks the splice and splices the fibers again. To repeat the splicing, however, the operator needs to cut both optical fibers some length away (usually a few centimeters or more) from the splice break point, and prepare (strip and cleave) the fibers again. As a result of cutting the fibers, the total fiber length shortens and the optical fiber needs to be re-routed. To be able to reroute the fiber without an essential change of the fiber path within the device, the fiber is usually placed in loops within the device. For repeating the splicing operation, a length of the optical fiber, approximately equal to one loop length, is cut from both fibers being spliced, and the splicing operation is repeated. It is a good practice to loop the fibers at least three times on both sides of the splice point, to be able to repeat the splicing operation three times if so required.
Yet another packaging requirement of optical fibers results from a well-known “springing” property of optical fibers. Even thin singlemode fibers have a tendency to straighten when left unattached to a tray or a mount. Although some “memory” of previous fiber coiling is present, the fiber usually does not simply stay bent as most electrical wires would. This calls for restraining the optical fiber within the device using clips and bobbins.
Yet another packaging requirement of optical fibers results from sensitivity of optical performance of most optical fibers to a sharp mechanical stress, which is especially true for polarization-maintaining fibers. The optical fiber must be mechanically restrained in such a manner as to avoid sharp stress points on the fiber surface. In many cases, it is also preferable to prevent the optical fiber from randomly moving within the device.
One of the simplest and most frequently used methods of routing an optical fiber within a device includes coiling the fiber on a flat surface such as a printed circuit board, using multiple clips or clamps attached to the flat surface along the fiber path for restraining the fiber. Although simple, this method does not prevent the fiber from moving because the clips usually allow for some leeway to prevent sharp stresses on the fiber, which are detrimental as noted above. Furthermore, the fiber can easily get entangled in the clips during routing, and different operators can use the same clip patterns to route the fiber slightly differently or even completely differently, which impacts reproducibility and reworkability of the devices.
Another frequently used method is to use a fiber spool or bobbin for coiling the fiber. Referring to FIG. 1, a prior-art optoelectronic device 1 is shown including a printed circuit board 8 having mounted thereupon electrical connectors 12 and 14, standoffs 11, two electro-optical components 6, a bobbin 16, and two fiber connectors 2. The electro-optical components 6 are fiber coupled with optical fiber 4 through stress-relieving elements 5. The optical fiber 4 is wound on the bobbin 16. The optical fiber 4 is held in place on the bobbin 16 using fasteners 38. A detailed description of the optoelectronic device 1 is provided by Vanderhoof et al. in U.S. Pat. No. 6,208,797, which is incorporated herein by reference.
Disadvantageously, the bobbin 16 cannot prevent the optical fiber 4 from moving at locations where the optical fiber 4 is not wound on the bobbin 16. Furthermore, the bobbin 16 occupies valuable space on the printed circuit board 8, as well as large overall volume over the printed circuit board 8. In fact, a volume occupied by a prior-art bobbin, such as the bobbin 16, can be at least an order of magnitude greater than the volume occupied by the optical fiber 4 wound on the bobbin 16. Fiber bobbins disclosed by Grant et al. in U.S. Pat. No. 5,142,661 and by DeMeritt et al. in U.S. Pat. No. 5,659,641, incorporated herein by reference, have similar drawbacks.
Rawlings in U.S. Pat. No. 5,469,526, incorporated herein by reference, discloses an optical fiber support in form of an oval “raceway” for guiding an optical fiber. Disadvantageously, the optical fiber support of Rawlings does not provide an adequate means for immobilizing the fiber within the raceway. Also, the raceway of Rawlings takes a large fraction of the overall volume within a package of the device.
One method to immobilize an optical fiber without introducing an excessive mechanical stress is to use an adhesive surface with a tacky or a pressure-sensitive adhesive or simply using a single- or a double-sided sticky tape. Such an approach is disclosed, for example, by Parstorfer in U.S. Pat. No. 4,753,509, which is incorporated herein by reference, wherein an optical fiber is immobilized near fiber splice regions using “adhesive holding zones” placed near the fiber splices. Disadvantageously, the method of Parstorfer does little to immobilize the optical fiber in other regions of the device.
The prior art is lacking a fiber tray that supports and immobilizes the optical fiber substantially along its entire length within the device while providing a repeatable routing of the optical fiber along a uniquely defined path, without having to occupy a considerable height or volume inside the package. Accordingly, it is a goal of the present invention to provide such a fiber tray. Furthermore, a fiber tray of the invention, while being thin, allows for easy fiber rerouting after the fiber length has changed due to re-splicing.